9
iv Where a single pipe serves a number of discharges, such as in blocks
of ats, the number served should be limited to not more than 6 systems
so that any installation discharging can be traced reasonably easily. The
single common discharge pipe should be at least one pipe size larger
than the largest individual discharge pipe (D2) to be connected. If
unvented hot water storage systems are installed where discharges
from safety devices may not be apparent i.e. in dwellings occupied by
blind, inrm or disabled people, consideration should be given to the
installation of an electronically operated device to warn when discharge
takes place.
NOTE:The discharge will consist of scalding water and steam. Asphalt,
roong felt and non-metallic rainwater goods may be damaged by such
discharges.
WORKED EXAMPLE OF DISCHARGE PIPE SIZING:
The example below is for a G½” temperature relief valve with a discharge
pipe (D2) having 4 No. elbows and length of 7m from the tundish to the
point of discharge.
From Table 1 (below):
• Maximum resistance allowed for a straight length of 22mm copper
discharge pipe (D2) from a G½” temperature relief valve is 9.0m.
• Subtract the resistance for 4 No. 22mm elbows at 0.8m each = 3.2m
• Therefore the permitted length equates to: 5.8m
• 5.8m is less than the actual length of 7m therefore calculate the next
largest size.
• Maximum resistance allowed for a straight length of 28mm pipe (D2)
from a G1/2 temperature relief valves equates to 18m.
• Subtract the resistance of 4 No. 28mm elbows at 1.0m each = 4.0m
Therefore the maximum permitted length equates to: 14m
• As the actual length is 7m, a 28mm (D2) copper pipe will be satisfactory.
TABLE 01: SIZING OF COPPER DISCHARGE PIPE (D2) FOR COMMON
T & P RELIEF VALVE SIZES.
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